U.S. patent application number 14/345213 was filed with the patent office on 2015-10-08 for tire tread.
This patent application is currently assigned to MICHELIN RECHERCHE ET TECHNIQUE S.A.. The applicant listed for this patent is Xavier Saintigny, Raymond Stubblefield. Invention is credited to Xavier Saintigny, Raymond Stubblefield.
Application Number | 20150283854 14/345213 |
Document ID | / |
Family ID | 47883575 |
Filed Date | 2015-10-08 |
United States Patent
Application |
20150283854 |
Kind Code |
A1 |
Saintigny; Xavier ; et
al. |
October 8, 2015 |
TIRE TREAD
Abstract
Treads and tires having such treads having improved
characteristics breaking the compromise between Wear and wet
braking, such treads manufactured from a rubber composition that
may include greater than 90 phr of an elastomer component selected
from styrene-butadiene rubber (SBR), a polybutadiene or
combinations thereof having, a glass transition temperature of
between -100.degree. C. and less than -50.degree. C. and a
plasticizing system. The plasticizing system may include, for
example, between 5 phr and 120 phr of a plasticizing resin having a
Tg of at least 25.degree. C. and between 0 phr and 60 phr of a
plasticizing liquid. Particular embodiments may include the
elastomer component having a Tg of between -90.degree. C. and
-60.degree. C. and/or may further have the elastomer component
included in an amount of at least 95 phr.
Inventors: |
Saintigny; Xavier;
(Greenville, SC) ; Stubblefield; Raymond;
(Greenville, SC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Saintigny; Xavier
Stubblefield; Raymond |
Greenville
Greenville |
SC
SC |
US
US |
|
|
Assignee: |
MICHELIN RECHERCHE ET TECHNIQUE
S.A.
Granges-Paccot
CH
COMPAGNIE GENERALE DES ETABLISSEMENTS MICHELIN
Clermont-Ferrand
FR
|
Family ID: |
47883575 |
Appl. No.: |
14/345213 |
Filed: |
September 14, 2011 |
PCT Filed: |
September 14, 2011 |
PCT NO: |
PCT/US11/51644 |
371 Date: |
March 14, 2014 |
Current U.S.
Class: |
524/313 |
Current CPC
Class: |
C08L 9/06 20130101; C08K
5/0016 20130101; C08K 5/0016 20130101; C08L 47/00 20130101; C08L
9/00 20130101; B60C 11/0008 20130101; B60C 2011/0025 20130101; C08K
5/0016 20130101; C08L 9/06 20130101; B60C 1/0016 20130101; C08L
9/00 20130101 |
International
Class: |
B60C 1/00 20060101
B60C001/00; C08L 47/00 20060101 C08L047/00; C08L 9/00 20060101
C08L009/00; B60C 11/00 20060101 B60C011/00; C08L 9/06 20060101
C08L009/06 |
Claims
1. A tread for a tire, the tread comprising a rubber composition
that is based upon a cross-linkable elastomer composition, the
cross-linkable elastomer composition comprising, per 100 parts by
weight of rubber (phr): greater than 90 phr of an elastomer
component selected from a styrene-butadiene rubber, a polybutadiene
rubber or combinations thereof having a glass transition
temperature of between -100.degree. C. and less than -50.degree.
C.; between 0 phr and 9 phr of an additional highly unsaturated
diene elastomer; a plasticizing system comprising between 5 phr and
120 phr of a plasticizing resin having a Tg of at least 25.degree.
C. and between 0 phr and 60 phr of a plasticizing liquid; a
reinforcing filler; and a curing system.
2. The tread of claim 1, wherein the plasticizing system comprises
between 10 phr and 55 phr of the plasticizing liquid.
3. The tread of claim 1, wherein the plasticizing system comprises
between 55 phr and 120 phr of the plasticizing resin.
4. The tread of claim 1, wherein the cross-linkable rubber
composition comprises between 0 phr and 5 phr of the additional
highly unsaturated diene elastomer.
5. The tread of claim 1, wherein the cross-linkable rubber
composition comprises 0 phr of the additional highly unsaturated
diene elastomer.
6. The tread of claim 1, wherein the glass transition temperature
of the elastomer component is between -100.degree. C. and
-55.degree. C.
7. The tread of claim 1, wherein the glass transition temperature
of the elastomer component is between -90.degree. C. and
-60.degree. C.
8. The tread of claim 1, wherein a glass transition temperature of
the rubber composition is between -30.degree. C. and -10.degree.
C.
9. The tread of claim 1, wherein the shear modulus G* of the rubber
composition is between 0.6 MPa and 1.1 MPa.
10. The tread of claim 1, wherein the elastomer component, the
additional highly unsaturated diene rubber or combinations thereof
are functionalized with an active moiety.
11. The tread of claim 10, wherein the elastomer component includes
chain ends having a silanol functional group attached as the active
moiety.
12. The tread of claim 1, wherein the reinforcing filler is silica,
the rubber composition comprising between 90 phr and 130 phr of the
silica.
13. The tread of claim 1, wherein the plasticizing resin has a
glass transition temperature of between 40.degree. C. and
85.degree. C.
14. The tread of claim 11, wherein the plasticizing resin is a
polylimonene resin.
15. The tread of claim 1, wherein the rubber composition comprises
between 20 phr and 70 phr of the plasticizing resin.
16. The tread of claim 1, wherein the plasticizing liquid is a
selected from sunflower oil, soybean oil, safflower oil, corn oil,
linseed oil, cotton seed oil or combinations thereof.
17. The tread of claim 15, wherein the plasticizing liquid has an
oleic content of at least 80 wt. %.
18. The tread of claim 1, wherein the rubber composition comprises
between 10 phr and 50 phr of the plasticizing liquid.
19. The tread of claim 1, wherein the rubber composition has a
glass transition temperature of between -28.degree. C. and
-14.degree. C.
20. The tread of claim 1, wherein the rubber composition has a
shear modulus G* measured at 60.degree. C. of between 0.5 MPa and
1.5 MPa.
21. The tread of claim 1, wherein the elastomer component is 100
phr of the styrene-butadiene rubber.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates generally to vehicle tires and more
particularly, to tire treads and materials from which they are
made.
[0003] 2. Description of the Related Art
[0004] It is known in the industry that tire designers must often
compromise on certain characteristics of the tires they are
designing. Changing a tire design to improve one characteristic of
the tire will often result in a compromise; i.e., an offsetting
decline in another tire characteristic. One such comprise exists
between tire wear and wet braking. Tire wear may be improved by
increasing the amount of polybutadiene blended into the tread's
rubber composition. However, increasing the polybutadiene content
in the tread's rubber composition typically results in a loss of
the wet braking performance that is known to be improved, for
example, by decreasing the polybutadiene content of the tire
tread.
[0005] Tire designers and those conducting research in the tire
industry search for materials and tire structures that can break
some of the known compromises. It would be desirable to provide new
tire designs that break the compromise between wear and wet
braking.
SUMMARY OF THE INVENTION
[0006] Particular embodiments of the present invention include
treads and tires having such treads that have improved
characteristics breaking the compromise between wear and wet
braking. Such embodiments include a tread for a tire comprising a
rubber composition based upon a cross-linkable composition having
greater than 90 phr of an elastomer component selected from
styrene-butadiene rubber (SBR), polybutadiene rubber or
combinations thereof having a glass transition temperature of
between -100.degree. C. and less than -50.degree. C. and a
plasticizing system. Embodiments include having a plasticizing
system comprising between 5 phr and 120 phr of a plasticizing resin
having a Tg of at least 25.degree. C. and between 0 phr and 60 phr
of a plasticizing oil.
[0007] There may be embodiments that include between 0 phr and 9
phr of an additional highly unsaturated diene elastomer blended
into the cross-linkable rubber composition as well as a reinforcing
filler. The cross-linkable rubber composition may further include a
curing system.
[0008] Particular embodiments may include the elastomer component
having a Tg of between -90.degree. C. and -60.degree. C. and/or may
further have the elastomer component included in an amount of at
least 95 phr.
[0009] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more detailed
descriptions of particular embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a graph that compares the wet braking and wear
performance for tires having treads manufactured from different
rubber compositions.
DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS
[0011] Particular embodiments of the present invention include
tires and treads for vehicles that surprisingly break a compromise
faced by tire designers; i.e., an increase in the tread wear of a
tire often results in a decrease in the wet braking performance of
the tire. This compromise may be broken by forming unique tire
treads from a rubber composition that includes a rubber component
having a low glass transition temperature (Tg) of between
-100.degree. C. and less than -50.degree. C. and a plasticizing
system that may include both a high loading of a plasticizing resin
having a high Tg and a plasticizing liquid.
[0012] The tires and treads disclosed herein are formed of a rubber
composition that includes a rubber component that is made up
entirely or almost entirely of a rubber having a low glass
transition temperature (Tg), i.e., between -100.degree. C. and less
than -50.degree. C. Such useful rubber components may include, for
example, SBR, polybutadiene or combinations thereof. While
particular embodiments of the present invention may utilize only
the low Tg rubber as the rubber component of a rubber composition,
other embodiments may include up to 9 parts by weight per hundred
parts of rubber (phr) of one or more other diene rubbers blended
into the rubber composition. As will be shown below, it is this
exclusive or nearly exclusive use of the low Tg rubber as the
elastomer component in the rubber composition mixed with a high Tg
resin that surprisingly provides the tread's high performance level
for both wet braking and wear.
[0013] As used herein, "phr" is "parts per hundred parts of rubber
by weight" and is a common measurement in the art wherein
components of a rubber composition are measured relative to the
total weight of rubber in the composition, i.e., parts by weight of
the component per 100 parts by weight of the total rubber(s) in the
composition.
[0014] As used herein, elastomer and rubber are synonymous
terms.
[0015] As used herein, "based upon" is a term recognizing that
embodiments of the present invention are made of vulcanized or
cured rubber compositions that were, at the time of their assembly,
uncured. The cured rubber composition is therefore "based upon" the
uncured rubber composition. In other words, the cross-linked rubber
composition is based upon or comprises the constituents of the
cross-linkable rubber composition.
[0016] As is known generally, a tire tread is the road-contacting
portion of a vehicle tire that extends circumferentially about the
tire. It is designed to provide the handling characteristics
required by the vehicle; e.g., traction, dry braking, wet braking,
cornering and so forth--all being preferably provided with a
minimum amount of noise being generated and at a low rolling
resistance.
[0017] Treads of the type that are disclosed herein include tread
elements that are the structural features of the tread that contact
the ground. Such structural features may be of any type or shape,
examples of which include tread blocks and tread ribs. Tread blocks
have a perimeter defined by one or more grooves that create an
isolated structure in the tread while a rib runs substantially in
the longitudinal (circumferential) direction and is not interrupted
by any grooves that run in the substantially lateral direction or
any other grooves that are oblique thereto.
[0018] The radially outermost faces of these tread elements make up
the contact surface of the tire tread--the actual surface area of
the tire tread that is adapted for making contact with the road as
the tire rotates. The total contact surface of the tire tread is
therefore the total surface area of all the radially outermost
faces of the tread elements that are adapted for making contact
with the road.
[0019] As noted above, particular embodiments of the present
invention include treads and tires having such treads manufactured
from a rubber composition that includes greater than 90 phr of a
low Tg rubber and between 0 phr and 9 phr of an additional highly
unsaturated diene elastomer. Alternatively the additional highly
unsaturated diene elastomer may be included at between 0 phr and 9
phr, between 0 phr and 5 phr or, in the case of the rubber
composition having only the low Tg rubber, 0 phr of the additional
highly unsaturated diene elastomer or any other type of diene
elastomer.
[0020] SBR is a copolymer of styrene and butadiene and is one of
the most commonly used rubbers. It is typically manufactured by one
of two processes--an emulsion process producing E-SBR and a
solution process producing S-SBR. Particular embodiments of the
present invention contemplate utilizing S-SBR, E-SBR or
combinations thereof as the low Tg SBR component of the rubber
composition.
[0021] The microstructure of SBR is typically described in terms of
the amount of bound styrene and the form of the butadiene portion
of the polymer. A typical SBR that is often suitable for use in
tires is around 25 wt. % bound styrene. Materials having a very
high content of bound styrene, e.g., around 80 wt. %, are
identified as high styrene resins and are not suitable as an
elastomer for manufacturing treads. Particular embodiments of the
present invention may utilize an SBR having a bound styrene content
of between 3 wt. % and 35 wt. % or alternatively between 3 wt. %
and 30 wt. %, between 3 wt. % and 25 wt. %, between 3 wt. % and 15
wt. %, between 5 wt. % and 20 wt. % or between 5 wt. % and 15 wt. %
bound styrene.
[0022] Because of the double bond present in the butadiene portion
of the SBR, the butadiene portion is made up of three forms:
cis-1,4, trans-1,4 and vinyl-1,2. SBR materials suitable for use as
the low Tg SBR may be described as having a vinyl-1,2-bond content
of between 4 mol. % and 30 mol. % or alternatively, between 4 mol.
% and 25 mol. % or between 4 mol. % and 20 mol. %.
[0023] As known to those having ordinary skill in the art, the
processing conditions under which the polymerization takes place
determines the microstructure of the SBR product. Typically, as the
styrene content and the vinyl content of the SBR increases, the Tg
of the material increases. To provide a tire tread having the
improved performance in the compromise between wear and wet
braking, the SBR that is exclusively or almost exclusively used in
the treads disclosed herein has a glass transition temperature of
less than -50.degree. C. or alternatively, less than -60.degree. C.
In particular embodiments, the SBR may have a glass transition
temperature of between -100.degree. C. and -50.degree. C. or
alternatively, between -100.degree. C. and -55.degree. C., between
-100.degree. C. and -60.degree. C. or between -90.degree. C. and
-50.degree. C. The glass transition temperature may also range
between greater than -80.degree. C. and -55.degree. C., between
-75.degree. C. and -60.degree. C. or between -75.degree. C. and
-65.degree. C. Glass transition temperatures for the low Tg SIR are
determined by differential scanning calorimetry (DSC) according to
ASTM E1356.
[0024] Examples of SBR having a low Tg include, for example,
DURADENE 711 (18% styrene, 12% vinyl, -70.degree. C. Tg) and
DURADENE 741 (5% styrene, 28% vinyl, -77.degree. C. Tg, tin coupled
polymer) that are available from Firestone of Akron, Ohio and
TUFDENE 1000 (18% styrene, 11% vinyl, -72.degree. C. Tg) available
from Asahi Chemical Company of Japan.
[0025] Polybutadienes that have glass transition temperatures in
the same ranges as the low Tg SBR materials described above may
also be utilized similarly to the low Tg SBR. The glass transition
temperatures of polybutadiene may be adjusted by varying the vinyl
content of the polymer using methods that are well known in the
art. Particular embodiments of the rubber compositions disclosed
herein may include greater than 90 phr or alternatively, greater
than 95 phr or 100 phr of a low Tg SBR, a low Tg polybutadiene,
i.e., a polybutadiene having the same glass transition temperature
ranges as defined above for a low Tg SBR, or combinations
thereof.
[0026] In addition to the low Tg SBR and/or polybutadiene
elastomers discussed above, particular embodiments of the present
invention may further include an additional diene elastomer. The
diene elastomers or rubbers that are useful for such rubber
compositions are understood to be those elastomers resulting at
least in part, i.e., a homopolymer or a copolymer, from diene
monomers, i.e., monomers having two double carbon-carbon bonds,
whether conjugated or not.
[0027] These diene elastomers may be classified as either
"essentially unsaturated" diene elastomers or "essentially
saturated" diene elastomers. As used herein, essentially
unsaturated diene elastomers are diene elastomers resulting at
least in part from conjugated diene monomers, the essentially
unsaturated diene elastomers having a content of such members or
units of diene origin (conjugated dienes) that is at least 15 mol.
%. Within the category of essentially unsaturated diene elastomers
are highly unsaturated diene elastomers, which are diene elastomers
having a content of units of diene origin (conjugated diene) that
is greater than 50 mol. %.
[0028] Those diene elastomers that do not fall into the definition
of being essentially unsaturated are, theretofore, the essentially
saturated diene elastomers. Such elastomers include, for example,
butyl rubbers and copolymers of dienes and of alpha-olefins of the
EPDM type. These diene elastomers have low or very low content of
units of diene origin (conjugated dienes), such content being less
than 15 mol. %.
[0029] The elastomers may have any microstructure, which is a
function of the polymerization conditions used, in particular of
the presence or absence of a modifying and/or randomizing agent and
the quantities of modifying and/or randomizing agent used. The
elastomers may, for example, be block, random, sequential or
micro-sequential elastomers, and may be prepared in dispersion or
in solution; they may be coupled and/or starred or alternatively
functionalized with a coupling and/or starring or functionalizing
agent. Of course these comments also apply to the low Tg SBR and
polybutadienes discussed above that are useful in the present
invention.
[0030] Functionalized rubbers, i.e., those appended with active
moieties, are well known in the industry. The backbone or the
branch ends of the elastomers may be functionalized by attaching
these active moieties to the ends of the chains or to the backbone
of the polymer Examples of functionalized elastomers include
silanol or polysiloxane end-functionalized elastomers, examples of
which may be found in U.S. Pat. No. 6,013,718, issued Jan. 11,
2000, which is hereby fully incorporated by reference. Other
examples of functionalized elastomers include those having
alkoxysilane groups as described in U.S. Pat. No. 5,977,238,
carboxylic groups as described in U.S. Pat. No. 6,815,473 or
polyether groups as described in U.S. Pat. No. 6,503,973, all these
cited patents being incorporated herein by reference. As noted,
such functionalized elastomers are also useful as the low Tg SBR
and polybutadiene rubbers as well.
[0031] Examples of suitable diene elastomers include
polybutadienes, particularly those having a content of 1,2-units of
between 4 mol. % and 80 mol. % or those having a cis-1,4 content of
more than 80 mol. %. Also included are polyisoprenes and
butadiene/isoprene copolymers, particularly those having an
isoprene content of between 5 wt. % and 90 wt. % and a glass
transition temperature (Tg, measured in accordance with ASTM D3418)
of -40.degree. C. to -80.degree. C.
[0032] In summary, suitable diene elastomers for particular
embodiments of the present invention include highly unsaturated
diene elastomers such as polybutadienes (BR), polyisoprenes (IR),
natural rubber (NR), butadiene copolymers, isoprene copolymers and
mixtures of these elastomers. Such copolymers include
butadiene/styrene copolymers (SBR), isoprene/butadiene copolymers
(BIR), isoprene/styrene copolymers (SIR) and
isoprene/butadiene/styrene copolymers (SBIR). Suitable elastomers
may also include any of these elastomers being functionalized
elastomers.
[0033] The additional diene elastomer included in particular
embodiments of the present invention may be one diene elastomer or
a mixture of several diene elastomers. The additional diene
elastomer may further be selected from the highly unsaturated diene
elastomers, the essentially unsaturated diene elastomers, the
essentially saturated diene elastomers or combinations thereof.
[0034] In addition to the rubber, the rubber composition disclosed
herein may further include reinforcing filler. Reinforcing fillers
are added to rubber compositions to, inter alia, improve their
tensile strength and wear resistance. Any suitable reinforcing
filler may be suitable for use in compositions disclosed herein
including, for example, carbon blacks and/or inorganic reinforcing
fillers such as silica, with which a coupling agent is typically
associated.
[0035] Suitable carbon blacks include, for example, those of the
type HAF, ISAF and SAF, conventionally used in tires. Reinforcing
blacks of ASTM grade series 100, 200 and/or 300 are suitable such
as, for example, the blacks N115, N134, N234, N330, N339, N347,
N375 or alternatively, depending on the intended application,
blacks of higher ASTM grade series such as N660, N683 and N772.
[0036] Inorganic reinforcing fillers include any inorganic or
mineral fillers, whatever its color or origin (natural or
synthetic), that are capable without any other means, other than an
intermediate coupling agent, or reinforcing a rubber composition
intended for the manufacture of tires. Such inorganic reinforcing
fillers can replace conventional tire-grade carbon blacks, in whole
or in part, in a rubber composition intended for the manufacture of
tires. Typically such fillers may be characterized as having the
presence of hydroxyl (--OH) groups on its surface.
[0037] Inorganic reinforcing fillers may take many useful forms
including, for example, as powder, microbeads, granules, balls
and/or any other suitable form as well as mixtures thereof.
Examples of suitable inorganic reinforcing fillers include mineral
fillers of the siliceous type, such as silica (SiO.sub.2), of the
aluminous type, such as alumnina (AlO.sub.3) or combinations
thereof.
[0038] Useful silica reinforcing fillers known in the art include
finned, precipitated and/or highly dispersible silica (known as
"HD" silica). Examples of highly dispersible silicas include
Ultrasil 7000 and Ultrasil 7005 from Degussa, the silicas Zeosil
1165MP, 1135MP and 1115MP from Rhodia, the silica Hi-Sil EZ150G
from PPG and the silicas Zeopol 8715, 8745 and 8755 from Huber. In
particular embodiments, the silica may have a BET surface area, for
example, of between 60 m.sup.2/g and 250 m.sup.2/g or alternatively
between 80 m.sup.2/g and 230 m.sup.2/g.
[0039] Examples of useful reinforcing aluminas are the aluminas
Baikalox A125 or CR125 from Baikowski, APA-100RDX from Condea,
Aluminoxid C from Degussa or AKP-G015 from Sumitomo Chemicals.
[0040] For coupling the inorganic reinforcing filler to the diene
elastomer, a coupling agent that is at least bifunctional provides
a sufficient chemical and/or physical connection between the
inorganic reinforcement filler and the diene elastomer. Examples of
such coupling agents include bifunctional organosilanes or
polyorganosiloxanes. Such coupling agents and their use are well
known in the art. The coupling agent may optionally be grafted
beforehand onto the diene elastomer or onto the inorganic
reinforcing filler as is known. Otherwise it may be mixed into the
rubber composition in its free or non-grafted state. One useful
coupling agent is X 50-S, a 50-50 blend by weight of Si69 (the
active ingredient) and N330 carbon black, available from Evonik
Degussa.
[0041] In the rubber compositions according to the invention, the
coupling agent may be included at any suitable amount for the given
application, examples of which are between 2 phr and 15 phr or
alternatively, between 2 phr and 12 phr. It is generally desirable
to minimize its use. In particular embodiments, the amount of
coupling agent may represent between 0.5 and 15 wt. % relative to
the total weight of the silica filler. In the case for example of
tire treads for passenger vehicles, the coupling agent may be less
than 12 wt. % or even less than 8 wt. % relative to the total
weight of the silica filler.
[0042] In particular embodiments, the amount of total reinforcing
filler (carbon black and/or reinforcing inorganic filler) may
include any suitable amount for the given application, examples of
which are between 20 phr and 200 phr or alternatively between 30
phr and 150 phr, between 90 phr and 130 phr or between 50 phr and
175 phr.
[0043] In addition to the diene elastomer and reinforcing filler,
particular embodiments of the rubber composition disclosed herein
may further include a plasticizing system. The plasticizing system
may provide both an improvement to the processability of the rubber
mix and/or a means for adjusting the rubber composition's glass
transition temperature and/or its rigidity. Suitable plasticizing
systems may include a plasticizing liquid, a plasticizing resin or
combinations thereof.
[0044] Suitable plasticizing liquids may include any liquid known
for its plasticizing properties with diene elastomers. At room
temperature (23.degree. C.), these liquid plasticizers or these
oils of varying viscosity are liquid as opposed to the resins that
are solid. Examples include those derived from petroleum stocks,
those having a vegetable base and combinations thereof. Examples of
oils that are petroleum based include aromatic oils, paraffinic
oils, naphthenic oils, MES oils, TDAE oils and so forth as known in
the industry. Also known are liquid diene polymers, the polyolefin
oils, ether plasticizers, ester plasticizers, phosphate
plasticizers, sulfonate plasticizers and combinations of liquid
plasticizers.
[0045] Examples of suitable vegetable oils include sunflower oil,
soybean oil, safflower oil, corn oil, linseed oil and cotton seed
oil. These oils and other such vegetable oils may be used
singularly or in combination. In some embodiments, sunflower oil
having a high oleic acid content (at least 70 weight percent or
alternatively, at least 80 weight percent) is useful, an example
being AGRI-PURE 80, available from Cargill with offices in
Minneapolis, Minn. In particular embodiments of the present
invention, the selection of a suitable plasticizing oil is limited
to a vegetable oil having a high oleic acid content.
[0046] The amount of plasticizing liquid useful in any particular
embodiment of the present invention depends upon the particular
circumstances and the desired result. In general, for example, the
plasticizing liquid may be present in the rubber composition in an
amount of between 0 or 10 phr and 60 phr or alternatively, between
0 or 10 phr and 55 phr, between 0 or 10 phr and 50 phr, between 0
or 5 phr and 40 phr or between 0 or 10 phr and 35 phr. In
particular embodiments, there may be no plasticizing liquid
utilized.
[0047] A plasticizing hydrocarbon resin is a hydrocarbon compound
that is solid at ambient temperature (e.g., 23.degree. C.) as
opposed to a liquid plasticizing compound, such as a plasticizing
oil. Additionally a plasticizing hydrocarbon resin is compatible,
i.e., miscible, with the rubber composition with which the resin is
mixed at a concentration that allows the resin to act as a true
plasticizing agent, e.g., at a concentration that is typically at
least 5 plh (parts per hundred parts rubber by weight).
[0048] Plasticizing hydrocarbon resins are polymers that can be
aliphatic, aromatic or combinations of these types, meaning that
the polymeric base of the resin may be formed from aliphatic and/or
aromatic monomers. These resins can be natural or synthetic
materials and can be petroleum based, in which case the resins may
be called petroleum plasticizing resins, or based on plant
materials. In particular embodiments, although not limiting the
invention, these resins may contain essentially only hydrogen and
carbon atoms.
[0049] The plasticizing hydrocarbon resins useful in particular
embodiment of the present invention include those that are
homopolymers or copolymers of cyclopentadiene (CPD) or
dicyclopentadiene (DCPD), homopolymers or copolymers of terpene,
homopolymers or copolymers of C.sub.5 cut and mixtures thereof.
[0050] Such copolymer plasticizing hydrocarbon resins as discussed
generally above may include, for example, resins made up of
copolymers of (D)CPD/vinyl-aromatic, of (D)CPD/terpene, of
(D)CPD/C.sub.5 cut, of terpene/vinyl-aromatic, of C.sub.5
cut/vinyl-aromatic and of combinations thereof.
[0051] Terpene monomers useful for the terpene homopolymer and
copolymer resins include alpha-pinene, beta-pinene and limonene.
Particular embodiments include polymers of the limonene monomers
that include three isomers: the L-limonene (laevorotatory
enantiomer), the D-limonene (dextrorotatory enantiomer), or even
the dipentene, a racemic mixture of the dextrorotatory and
laevorotatory enantiomers.
[0052] Examples of vinyl aromatic monomers include styrene,
alpha-methylstyrene, ortho-, meta-, para-methylstyrene,
vinyl-toluene, para-tertiobutylstyrene, methoxystyrenes,
chloro-styrenes, vinyl-mesitylene, divinylbcnzene,
vinylnaphthalene, any vinyl-aromatic monomer coming from the
C.sub.9 cut (or, more generally, from a C.sub.8 to C.sub.10 cut).
Particular embodiments that include a vinyl-aromatic copolymer
include the vinyl-aromatic in the minority monomer, expressed in
molar fraction, in the copolymer.
[0053] Particular embodiments of the present invention include as
the plasticizing hydrocarbon resin the (D)CPD homopolymer resins,
the (D)CPD/styrene copolymer resins, the polylimonene resins, the
limonene/styrene copolymer resins, the limonene/D(CPD) copolymer
resins, C.sub.5 cut/styrene copolymer resins, C.sub.5 cut/C.sub.9
cut copolymer resins, and mixtures thereof.
[0054] Commercially available plasticizing resins that include
terpene resins suitable for use in the present invention include a
polyalphapinene resin marketed under the name Resin R2495 by
Hercules Inc. of Wilmington, Del. Resin R2495 has a molecular
weight of about 932, a softening point of about 135.degree. C. and
a glass transition temperature of about 91.degree. C. Another
commercially available product that may be used in the present
invention includes DERCOLYTE L120 sold by the company DRT of
France. DERCOLYTE L120 polyterpene-limonene resin has a number
average molecular weight of about 625, a weight average molecular
weight of about 1010, an Ip of about 1.6, a softening point of
about 119.degree. C. and has a glass transition temperature of
about 72.degree. C. Still another commercially available terpene
resin that may be used in the present invention includes SYLVARES
TR 7125 and/or SYLVARES TR 5147 polylimonene resin sold by the
Arizona Chemical Company of Jacksonville, Fla. SYLVARES 7125
polylimonene resin has a molecular weight of about 1090, has a
softening point of about 125.degree. C., and has a glass transition
temperature of about 73.degree. C. while the SYLVARES TR 5147 has a
molecular weight of about 945, a softening point of about
120.degree. C. and has a glass transition temperature of about
71.degree. C.
[0055] Other suitable plasticizing hydrocarbon resins that are
commercially available include C.sub.5 cut/vinyl-aromatic styrene
copolymer, notably C.sub.5 cut/styrene or C.sub.5 cut/C.sub.9 cut
from Neville Chemical Company under the names SUPER NEVTAC 78,
SUPER NEVTAC 85 and SUPER NEVTAC 99; from Goodyear Chemicals under
the name WINGTACK EXTRA; from Kolon under names HIKOREZ T1095 and
HIKOREZ T1100; and from Exxon under names ESCOREZ 2101 and ECR
373.
[0056] Yet other suitable plasticizing hydrocarbon resins that are
limonene/styrene copolymer resins that are commercially available
include DERCOLYTE TS 105 from DRT of France; and from Arizona
Chemical Company under the name ZT115LT and ZT5100.
[0057] It may be noted that the glass transition temperatures of
plasticizing resins may be measured by Differential Scanning
Calorimetry (DCS) in accordance with ASTM D3418 (1999). In
particular embodiments, useful resins may be have a glass
transition temperature that is at least 25.degree. C. or
alternatively, at least 40.degree. C. or at least 60.degree. C. or
between 25.degree. C. and 95.degree. C., between 40.degree. C. and
85.degree. C. or between 60.degree. C. and 80.degree. C.
[0058] The amount of plasticizing hydrocarbon resin useful in any
particular embodiment of the present invention depends upon the
particular circumstances and the desired result. In general, for
example, the plasticizing hydrocarbon resin may be present in the
rubber composition in an amount of between 5 phr and 120 phr or
alternatively, between 5 phr and 100 phr or between 5 phr and 60
phr. In particular embodiments, the plasticizing hydrocarbon resin
may be present in an amount of between 5 phr and 70 phr, between 25
phr and 55 phr, between 20 phr and 70 phr, between 20 phr and 65
phr, between 25 phr and 65 phr, between 25 phr and 100 phr, between
55 and 120 phr, between 65 phr and 110 phr or between 15 phr and 70
phr.
[0059] The rubber compositions disclosed herein may be cured with
any suitable curing system including a peroxide curing system or a
sulfur curing system. Particular embodiments are cured with a
sulfur curing system that includes free sulfur and may further
include, for example, one or more of accelerators, stearic acid and
zinc oxide. Suitable free sulfur includes, for example, pulverized
sulfur, rubber maker's sulfur, commercial sulfur, and insoluble
sulfur. The amount of free sulfur included in the rubber
composition is not limited and may range, for example, between 0.5
phr and 10 phr or alternatively between 0.5 phr and 5 phr or
between 0.5 phr and 3 phr. Particular embodiments may include no
free sulfur added in the curing system but instead include sulfur
donors.
[0060] Accelerators are used to control the time and/or temperature
required for vulcanization and to improve the properties of the
cured rubber composition. Particular embodiments of the present
invention include one or more accelerators. One example of a
suitable primary accelerator useful in the present invention is a
sulfenamide. Examples of suitable sulfenamide accelerators include
n-cyclohexyl-2-benzothiazole sulfenamide (CBS),
N-tert-butyl-2-benzothiazole Sulfenamide (TBBS),
N-Oxydiethyl-2-benzthiazolsulfenamid (MBS) and
N'-dicyclohexyl-2-benzothiazolesulfenamide (DCBS). Combinations of
accelerators are often useful to improve the properties of the
cured rubber composition and the particular embodiments include the
addition of secondary accelerators.
[0061] Particular embodiments may include as a secondary accelerant
the use of a moderately fast accelerator such as, for example,
diphenylguanidine (DPG), triphenyl guanidine (TPG), diorthotolyl
guanidine (DOTG), o-tolylbigaunide (OTBG) or hexamethylene
tetramine (HMTA). Such accelerators may be added in an amount of up
to 4 phr, between 0.5 and 3 phr, between 0.5 and 2.5 phr or between
1 and 2 phr. Particular embodiments may exclude the use of fast
accelerators and/or ultra-fast accelerators such as, for example,
the fast accelerators: disulfides and benzothiazoles; and the
ultra-accelerators: thiurams, xanthates, dithiocarbamates and
dithiophosphates.
[0062] Other additives can be added to the rubber compositions
disclosed herein as known in the art. Such additives may include,
for example, some or all of the following: antidegradants,
antioxidants, fatty acids, waxes, stearic acid and zinc oxide.
Examples of antidegradants and antioxidants include 6PPD, 77PD,
IPPD and TMQ and may be added to rubber compositions in an amount,
for example, of from 0.5 phr and 5 phr. Zinc oxide may be added in
an amount, for example, of between 1 phr and 6 phr or
alternatively, of between 1.5 phr and 4 phr. Waxes may be added in
an amount, for example, of between 1 phr and 5 phr.
[0063] The rubber compositions that are embodiments of the present
invention may be produced in suitable mixers, in a manner known to
those having ordinary skill in the art, typically using two
successive preparation phases, a first phase of thermo-mechanical
working at high temperature, followed by a second phase of
mechanical working at lower temperature.
[0064] The first phase of thermo-mechanical working (sometimes
referred to as "non-productive" phase) is intended to mix
thoroughly, by kneading, the various ingredients of the
composition, with the exception of the vulcanization system. It is
carried out in a suitable kneading device, such as an internal
mixer or an extruder, until, under the action of the mechanical
working and the high shearing imposed on the mixture, a maximum
temperature generally between 120.degree. C. and 190.degree. C.,
more narrowly between 130.degree. C. and 170.degree. C., is
reached.
[0065] After cooling of the mixture, a second phase of mechanical
working is implemented at a lower temperature. Sometimes referred
to as "productive" phase, this finishing phase consists of
incorporating by mixing the vulcanization (or cross-linking) system
(sulfur or other vulcanizing agent and accelerator(s)), in a
suitable device, for example an open mill. It is performed for an
appropriate time (typically between 1 and 30 minutes, for example
between 2 and 10 minutes) and at a sufficiently low temperature
lower than the vulcanization temperature of the mixture, so as to
protect against premature vulcanization.
[0066] The rubber composition can be formed into useful articles,
including treads for use on vehicle tires. The treads may be formed
as tread bands and then later made a part of a tire or they be
formed directly onto a tire carcass by, for example, extrusion and
then cured in a mold. As such, tread bands may be cured before
being disposed on a tire carcass or they may be cured after being
disposed on the tire carcass. Typically a tire tread is cured in a
known manner in a mold that molds the tread elements into the
tread, including, e.g., the sipes molded into the tread blocks.
[0067] It is recognized that treads may be formed from only one
rubber composition or in two or more layers of differing rubber
compositions, e.g., a cap and base construction. In a cap and base
construction, the cap portion of the tread is made of one rubber
composition that is designed for contact with the road. The cap is
supported on the base portion of the tread, the base portion made
of a different rubber composition. In particular embodiments of the
present invention the entire tread may be made from the rubber
compositions as disclosed herein while in other embodiments only
the cap portions of the tread may be made from such rubber
compositions.
[0068] It is recognized that the contact surface of a tread block,
i.e., that portion of the tread block that contacts the road, may
be formed totally from the rubber composition having the low Tg as
disclosed herein, may be formed totally from another rubber
composition or may be formed as combinations thereof. For example,
a tread block may be formed as a composite of layered rubber
compositions such that half of the block laterally is a layer of
the low Tg rubber composition and the other half of the block
laterally is a layer of an alternative rubber composition. Such
construction would provide a tread block having 80 percent of its
contact surface formed of the low Tg rubber composition.
[0069] As such, in particular embodiments of the present invention,
at least 80 percent of the total contact surface of all the tread
blocks on a tread may be formed from the rubber composition having
the low Tg as disclosed herein. Alternatively, at least 90 percent,
at least 95 percent or 100 percent of the total contact surface of
all the tread blocks on a tread may be formed from such rubber
composition.
[0070] While the tire treads disclosed herein are suitable for many
types of vehicles, particular embodiments include tire treads for
use on vehicles such as passenger cars and/or light trucks. Such
tire treads are also useful for all weather tires, snow tires
and/or warm weather tires. As such, the properties of the cured
rubber compositions from which the treads disclosed herein may be
manufactured may have a glass transition temperature of between
-35.degree. C. and -25.degree. C. and/or alternatively, between
-28.degree. C. and -14.degree. C., between -30.degree. C. and
-16.degree. C. and/or between -16.degree. C. and 10.degree. C.
[0071] In particular embodiments, such rubber composition may
further be characterized as having a shear modulus G* measured at
60.degree. C. of between 0.5 MPa and 2 MPa or alternatively, 0.5
MPa and 1.5 MPa, between 0.5 MPa and 1.2 MPa or 0.6 MPa and 1.1
MPa.
[0072] The invention is further illustrated by the following
examples, which are to be regarded only as illustrations and not
delimitative of the invention in any way. The properties of the
compositions disclosed in the examples were evaluated as described
below and these utilized methods are suitable for measurement of
the claimed properties of the present invention.
[0073] Modulus of elongation (MPa) was measured at 10% (MA10) at a
temperature of 23.degree. C. based on ASTM Standard D412 on dumb
bell test pieces. The measurements were taken in the second
elongation; i.e., after an accommodation cycle. These measurements
are secant moduli in MPa, based on the original cross section of
the test piece.
[0074] Wet braking for a tire mounted on an automobile fitted with
an ABS braking system was determined by measuring the distance
necessary to go from 50 MPH to 0 MPH upon sudden braking on wetted
ground (asphalt concrete). A value greater than that of the
control, which is arbitrarily set to 100, indicates an improved
result, that is to say a shorter braking distance.
[0075] Wear resistance of a tire mounted on an automobile was
measured by subjecting the tire to actual on-road travel and
measuring its wear rate (mm of tread lost per 1000 miles) at
between 10,000 and 12,000 miles traveled. A value greater than that
of the control, arbitrarily set to 100, indicates an improved
result, that is to say less wear rate.
[0076] The maximum tan delta dynamic properties for the rubber
compositions were measured at 23.degree. C. on a Metravib Model
VA400 ViscoAnalyzer Test System in accordance with ASTM D5992-96.
The response of a sample of vulcanized material (double shear
geometry with each of the two 10 mm diameter cylindrical samples
being 2 mm thick) was recorded as it was being subjected to an
alternating single sinusoidal shearing stress at a frequency of 10
Hz under a controlled temperature of 23.degree. C. Scanning was
effected at an amplitude of deformation of 0.05 to 50% (outward
cycle) and then of 50% to 0.05% (return cycle). The maximum value
of the tangent of the loss angle tan delta (max tan .delta.) was
determined during the return cycle.
[0077] Dynamic properties (Tg and G*) for the rubber compositions
were measured on a Metravib Model VA400 ViscoAnalyzer Test System
in accordance with ASTM D5992-96. The response of a sample of
vulcanized material (double shear geometry with each of the two 10
mm diameter cylindrical samples being 2 mm thick) was recorded as
it was being subjected to an alternating single sinusoidal shearing
stress of a constant 0.7 MPa and at a frequency of 10 Hz over a
temperature sweep from -60.degree. C. to 100.degree. C. with the
temperature increasing at a rate of 1.5.degree. C./min. The shear
modulus G* at 60.degree. C. was captured and the temperature at
which the max tan delta occurred was recorded as the glass
transition temperature, Tg.
Example 1
[0078] Rubber compositions were prepared using the components shown
in Table 1. The amount of each component making up the rubber
compositions shown in Table 1 are provided in parts per hundred
parts of rubber by weight (phr). The microstructures and glass
transition temperatures of each S-SBR is also provided in Table
1.
[0079] The terpene resin was SYLVARES TR-5147, a polylimonene resin
available from Arizona Chemical, Savannah, Ga. The plasticizing oil
was naphthenic oil and/or sunflower oil. The silica was ZEOSIL 160,
a highly dispersible silica available from Rhodia having a BET of
160 m.sup.2/g. The plasticizing oil was AGRI-PURE 80. The silane
coupling agent was X 50-S available from Evonik Degussa. The
curative package included sulfur, accelerators, zinc oxide and
stearic acid.
TABLE-US-00001 TABLE 1 Rubber Formulations Formulations F1 F2 F3 F4
S-SBR 100 100 100 100 Tg, .degree. C. -12 -24 -48 -65 Styrene, wt.
% 44 25 26 15 Vinyl, mol. % 41 58 24 25 Silica 107 107 107 107
Plasticizing Oil 47.5 41.5 31 19 Polyterpene Resin 7.5 29.5 44.9
Silane Coupling Agent 17.12 17.12 17.12 17.12 Additivies (Wax &
6PPD) 3.4 4 3.4 3.4 Curing Package 8.1 8.4 8.1 8.1 Physical
Properties MA10 @ 23.degree. C. (MPa) 5.25 6.17 5.2 4.83 Modulus G*
@ 60.degree. C. 0.97 0.98 1.05 1.05 Max Tan Delta @ 23.degree. C.
0.36 0.35 0.37 0.34 Tg, .degree. C. -13 -17 -19 -18 Tire Tests Wet
Braking 131 130 127 125 Wear 56 60 82 96
[0080] The rubber formulations were prepared by mixing the
components given in Table 1, except for the sulfur and the
accelerators, in a Banbury mixer operating between 25 and 65 RPM
until a temperature of between 130.degree. C. and 170.degree. C.
was reached. The accelerators and sulfur were added in the second
phase on a mill. Vulcanization was effected at 150.degree. C. for
40 minutes. The formulations were then tested to measure their
physical properties, the results of which are shown in Table 1.
[0081] FIG. 1 is a graph that compares the wet braking and wear
performance for tires having treads manufactured from different
rubber compositions. Tires (Primacy MXV4 201/55R16) were
manufactured using each of the formulations F1-F4 shown in Table 1.
The tires were tested for their wet braking and wear performance in
accordance with the test procedures described above. As the glass
transition temperature of the SBR was lowered, the results clearly
demonstrate the surprising break in the wear/wet braking
compromise. Comparing the performance of the tires having treads
manufactured of the F1 and F4 formulations, the wear performance
increased by 71% while the wet braking performance decreased by
only 5%.
[0082] The terms "comprising," "including," and "having," as used
in the claims and specification herein, shall be considered as
indicating an open group that may include other elements not
specified. The term "consisting essentially of," as used in the
claims and specification herein, shall be considered as indicating
a partially open group that may include other elements not
specified, so long as those other elements do not materially alter
the basic and novel characteristics of the claimed invention. The
terms "a," "an," and the singular forms of words shall be taken to
include the plural form of the same words, such that the terms mean
that one or more of something is provided. The terms "at least one"
and "one or more" are used interchangeably. The term "one" or
"single" shall be used to indicate that one and only one of
something is intended. Similarly, other specific integer values,
such as "two," are used when a specific number of things is
intended. The terms "preferably," "preferred," "prefer,"
"optionally," "may," and similar terms are used to indicate that an
item, condition or step being referred to is an optional (not
required) feature of the invention. Ranges that are described as
being "between a and b" are inclusive of the values for "a" and
"b."
[0083] It should be understood from the foregoing description that
various modifications and changes may be made to the embodiments of
the present invention without departing from its true spirit. The
foregoing description is provided for the purpose of illustration
only and should not be construed in a limiting sense. Only the
language of the following claims should limit the scope of this
invention.
* * * * *